请问大家平常拍SADP时，曝光时间都是用多少秒(second)?

如果透射斑和衍射斑的强度差别不大，一般选11s或16s。如果有些衍射斑点比较弱，就要把C2散焦，选择长时间曝光，我最长用过64s。透射斑太亮，而且有弱的衍射斑，我就会用beam stop挡一下透射斑，用二次曝光。

我老师上课的时候有说拍SADP时的步骤如下:
1.    carry out column alignment, and insert the specimen into the electron beam path.
2.    depress the DIFF switch, and set the camera length to 250 cm with the SELECTOR switch.
Note: the camera length is displayed on the DIFF line on PAGE-1.
3.    manipulate the DIFF FOCUS knob so as to obtain the sharpest possible direct spot. If the pot is not at the center of the fluorescent screen, turn on the DEFLECTOR-PROJ switch and center the spot with the SHIFT knobs.
4.    depress the SAM/ROCK switch and select the desire field of view and magnification.
5.    insert the field limiting aperture into the electron beam path.
i.    Set the field limiting aperture assembly lever to the left side. If this cause the image disappear, reduce the magnification, and manipulate knobs 2 and 3 so as to align the aperture.
ii.    Select the desired aperture size with knob 1.
iii.    Focus the field limiting aperture image with the DIFF FOCUS knob.
iv.    Center the aperture image with knob 2 and 3.
6.    if necessary, record the image.
7.    remove the objective aperture from the electron beam path.
8.    depress the DIFF switch, and select the camera length between 10 cm and 250 cm with the SELECTOR switch.
9.    focus the diffraction pattern with the DIFF FOCUS knob.
10.    intercept the direct beam with the beam stopper knob.
11.    darken the diffraction pattern with th BRIGHTNESS knob to the extent that the pattern is just discernible on the fluorescent screen, and record the pattern by manual exposure. An exposure time of about 1 minute is recommended.
Note: if the direct spot is also to be recorded, remove the beam stopper
我不知道曝光时间是否真的如上面所说的An exposure time of about 1 minute is recommended??

我经常用的就是16s和22s，1min很少用到，除非有特别弱的斑点。

謝謝指教，我會試試看16 or 22 sec的

嗯，JEOL的2010说明书上好像是提到NBD可以用70s。
另外，介孔的衍射最好用8s曝光，因为中心斑和衍射斑距离实在太近了。

这个每台仪器不一样,实际使用的时间都不一样的

我只用底片拍过几次ZSM－5的衍射，一般都是把相机长度选到150cm，曝光11s或16s。

我觉得拍电子衍射经验很重要，不同的底片感光度也不一样，摸索一下就行了。